1. Field of the Invention
The present invention generally relates to an inkjet head, and more particularly relates to an inkjet head and a method of producing the inkjet head where an ink channel unit and a housing for holding the ink channel unit are formed by stacking metal plates.
2. Description of the Related Art
Conventional inkjet heads are intended to be used with inks that do not degrade the parts constituting the conventional inkjet heads and the adhesives bonding those parts together. In these years, however, inkjet heads have come to be used, for example, to produce liquid crystal displays and to form wiring patterns. For such industrial purposes, inks with strong acidity are used. Such inks may degrade channel plates of an inkjet head and adhesives bonding the channel plates together. To cope with this problem, inkjet heads having chemical resistance against strongly acidic inks are being developed.
For example, in one inkjet head, a chemical resistant stainless steel is used for all channel plates that form flow paths for ink (ink channels) and the channel plates are bonded together by diffusion bonding instead of by adhesives. In this case, channel plates can be produced at a low cost by etching. Also, channel plates made of the same stainless steel show a substantially uniform thermal expansion coefficient and therefore it becomes easier to bond the channel plates together by diffusion bonding at a high temperature.
In an inkjet head production method, a stainless steel plate used as a diaphragm plate is bonded by diffusion bonding onto another stainless steel plate in which pressure chambers are formed (see, for example, patent document 1).
According to a description in patent document 1, since no adhesive is used for bonding the above stainless plates together, pressure generated by a piezoelectric element in the produced inkjet head is not absorbed by an adhesive layer and therefore can be efficiently transmitted to the ink. In patent document 1, however, methods of bonding other parts are not described.
Patent document 2 discloses an inkjet head produced by using diffusion bonding (see patent document 2). However, in patent document 2, diffusion bonding is used for bonding only some of the parts constituting the disclosed inkjet head.
Patent document 3 discloses a method of producing an inkjet head where all of the channel plates are bonded together by diffusion bonding. In patent document 3, a pressure plate for holding an ink channel unit is also bonded by diffusion bonding. The channel plates described in patent document 3 are formed by pressing instead of etching.
[Patent document 1] Japanese Patent Application Publication No. 63-265647
[Patent document 2] Japanese Patent Application Publication No. 63-15755
[Patent document 3] Japanese Patent Application Publication No. 11-179900
In the inkjet head production method disclosed in patent document 1, diffusion bonding is used only for a part of the ink channel unit and other parts such as the housing are bonded by an adhesive. Therefore, in an inkjet head produced according to patent document 1, adhesive layers made of the adhesive may be degraded by a strongly acidic ink.
In the inkjet head production methods disclosed in patent documents 2 and 3, the thicknesses of stacked metal plates and the process of stacking the metal plates are not clearly described. Therefore, it seems difficult to accurately stack very thin metal plates with the disclosed production methods.
Also, in patent document 3, channel plates produced by pressing metal plates are used. However, if the channel plates are stacked and bonded together without removing burrs and without correcting distortion generated in the pressing process, adhesion between the channel plates or the bonding reliability may be reduced. Also, if only the areas where the burrs are formed are ground, the thickness of the ground areas may change and, as a result, the bonding reliability is reduced.
Meanwhile, a disadvantage of bonding metal plates by diffusion bonding is that it requires a long time. Also, in an inkjet apparatus, multiple inkjet heads are normally used and arranged in a row at certain intervals. Therefore, it is preferable to produce multiple inkjet heads at once by bonding multiple sets of parts in one process.
When bonding multiple sets of parts in one process, the difference in thickness of the parts is preferably within plus or minus 1 μm and therefore the parts must be processed with high precision. Also, to produce channel plates and housing plates with such high precision, for example, by pressing, many complicated steps are required. This, in turn, causes the production costs to increase.